the relationship between tuberculin response, bcg vaccine scar and asthma

recent studies have proposed that a decline in bacterial infections such as tuberculosis is a factor underlying the rising prevalence and severity of atopic disorder in developed countries. there are conflicting ideas about the inverse relationship between bcg (bacillus calmette-guerin) vaccination and asthma. stronger response to tuberculin test as an indicator of more potent th1 response is supposed to influence th2 modulated allergic reactions. bcg scar considered as an indicator of th1 - immunoresponse has been proposed to be smaller in asthmatic children in some studies. in a case-control study, 97 asthmatic and 97 control children younger than 5 years of age and bcg vaccinated at birth were tested with 5 units of tuberculin intradermaly. after 48-72 hours, the indurated area was measured in two diameters. mean while, the scar of bcg in both groups was measured. severity of asthma in the case group was recorded and categorized into mild, moderate and severe groups. the case group consisted of 63% boys and 37% girls and their tuberculin response was significantly smaller than that of the control (p=0.000), but no data supported the inverse relationship between the tuberculin response and severity of asthma (p=0.113). the scar of bcg was not significantly different in the asthmatic children with variable severity of asthma and control group (p=0.864). children with definite asthma had a significant weaker response to tuberculin. this might be an indication of less potent th1-reponse in allergic patients, but it was not associated with severity of asthma. no significant relationship between the size of bcg scar and asthma or its severity was found so perhaps bcg scar is not a sensitive indicator for development of asthma in future.